The present invention relates to a paper feeding method and paper feeder.
The present invention is applicable to a paper feeding method and a paper feeder which can separately feed set paper to a desired position without fail by preventing backward movement of paper from a position where a plurality of sheets of paper are separately fed one at a time to a pickup-impossible position.
The present invention is also applicable to a paper feeding method and a paper feeder, which feed paper (plain paper, cardboard, a card, an envelope, an OHP sheet, or other recording material) stacked on a tray one at a time to an image-forming apparatus, or the like.
A paper feeder, which sets a plurality of sheets of paper in a loaded state and feeds paper by separating and feeding paper one sheet at a time to a desired position, has hitherto been used heavily. This paper feeder feeds, e.g., an original (paper) loaded in an image reader, to an image reading position. Alternately, the paper feeder is set in an image-forming apparatus, and feeds recording paper to a position where an image is to be recorded and formed (hereinafter called an “image recording-and-forming position”).
The paper feeder of this type comprises: a feeding roller for downwardly feeding paper to be brought into pressed contact; a lift plate which is designed so as to be able to load a plurality of sheets of paper and which lifts or lowers a front edge thereof in a direction to come into contact with or out of contact from an outer peripheral surface of the feeding roller; and a retard roller (a separation roller) which comes into pressed contact with the outer peripheral surface of the feeding roller at a position downward of the front edge of the lift plate in a rotational direction and which is rotated so as to follow the feeding roller under the load exceeding the set value. This paper feeder enables the outer peripheral surface of the feeding roller to come into pressed contact with the front edge of paper on the lift plate, to thus directly pick up the paper. The paper is nipped between the feeding roller and the retard roller, thereby separating the paper one sheet at a time and feeding the thus-separated paper downwardly. Therefore, the paper feeder enables an attempt to reduce space and cost by omitting setting of a so-called pickup roller which picks up paper on the lift plate.
In the configuration of such a paper feeder, paper is fed downward as if it were withdrawn while being nipped between the feeding roller and the retard roller or the lift plate. Even after having been passed to a downward pair of rollers, the paper produces a great load. For this reason, in connection with the paper feeder set in the image-forming apparatus, it has been proposed to sequentially separate the lift plate and the retard roller from the feeding roller after the document has been passed to the pair of rollers downward of the feeding roller is described (see, e.g., Patent Document 1). Even in connection with the paper feeder provided in the image-forming apparatus, it is described to separate the lift plate and the retard roller from the feeding roller after a document has been passed to a pair of rollers downstream of the feeding roller (see, e.g., Patent Document 2).
Patent Document 1: JP-A-11-334917
Patent Document 2: JP-UM-A-5-89344
However, in such a conventional paper feeder, the lift plate usually has the function of lifting and lowering the front edge of paper in a pinchable manner between the lift plate and the feeding roller. If an attempt is made to provide the paper feeder with a mechanism for separating the paper from the feeding roller until arrival at the retard roller, the paper feeder must be provided with a special mechanism, as described in the above-described publications, which in turn adds to cost.
Here, the feeding roller rotates in a paper feeding direction while rotating the retard roller. In contrast, the paper fed by the feeding roller is fed to a desired position while being firmly nipped between a pair of transport rollers and a pair of gate rollers, both of which are disposed in downstream positions. For this reason, after paper has been passed to the pair of transport rollers and the pair of gate rollers, the chance of feeding accuracy of the paper being deteriorated can be lessened.
However, when the paper feeder attempts to feed paper to a processing position in the image-forming apparatus main body, there may arise a case where the feeding roller is stopped for reasons of processing of the image-forming apparatus main body. For instance, in order to make a gap (a so-called gap between sheets of paper) between a trailing edge of one sheet of paper and a front edge of a subsequent sheet of paper, the feeding roller is temporarily stopped. In particular, in the case of a paper feeder set in the image-forming apparatus, before being fed to the image recording-and-forming position, recording paper is temporarily stopped in synchronism with image-forming timing of the image-forming apparatus main body while being nipped between the pair of downstream gate rollers. At this time, thanks to recent miniaturization of equipment, in the case of a paper feeder whose path to a processing position of the image-forming apparatus main body is designed to be short, there may arise a case where the recording paper is temporarily stopped before passing through the nipping position existing between the feeding roller and the retard roller.
However, when the feeding roller is stopped while the retard roller and the lift plate remain in pressed contact with the feeding roller, load induced when the feeding roller is moved a short distance backward in reaction to stoppage of the retard roller is imparted to the feeding roller. At this time, when the front edge of paper on the lift plate remains in pressed contact with the outer peripheral surface of the feeding roller, force for backwardly moving the feeding roller is cumulatively exerted on the front edge of the paper. As a result, there arises so-called backward movement; that is, a phenomenon of paper being moved backwardly to such an extent that paper cannot be fed by bringing the paper into pressed contact with the outer peripheral surface of the feeding roller by means of the lift plate.
Accordingly, the present invention aims at providing an inexpensive paper feeder capable of reliably separating and feeding set paper to a desired position without provision of a mechanism for moving a separation roller, by preventing backward movement of paper to a position where separated feeding of paper is impossible, which would otherwise arise as a result of stoppage of a feeding roller.
Available paper feeding methods include a method for continuously feeding a plurality of sheets of paper without regard to the kind of paper while the lift plate is held in a pressing state, and a method for feeding paper by lifting or lowering the lift plate every time one sheet of paper is fed, without regard to the kind of paper.
According to the technique for continuously feeding a plurality of sheets of paper without regard to the kind of paper while the lift plate remains in a pressing state, when paper is cardboard (including a postal card, an envelope, an OHP sheet, and the like, in addition to the cardboard), the next sheet of paper becomes likely to move backward because of reaction of a torque limiter of a retard roller. Consequently, overlapping transfer of paper or transfer failure of paper becomes likely to arise.
In the meantime, according to the technique for feeding paper by lifting or lowering the lift plate every time one sheet of paper is fed without regard to the kind of paper, when paper is plain paper (including thin paper), the lift plate is lowered when the topmost paper is fed, whereby the paper is released from a supported state. Therefore, the paper trembles in the vicinity of a nipping section located between the paper feeding roller and the retard roller, thereby causing chattering sound (noise).
Another object of the present invention is to provide a paper feeding method and a paper feeder, which enable reliable feeding of cardboard one at a time simultaneously with feeding of plain paper without causing chattering sound.